The present invention relates generally to fluid seals, and more particularly to shaft seals having a membrane sealing surface which provides pumping action in both directions of shaft rotation.
Conventional oil seals include a rigid casing portion and an elastomeric sealing lip. The primary lip is comprised of a pair of frusto-conical surfaces, xe2x80x9coilxe2x80x9d and xe2x80x9cairxe2x80x9d side surfaces, which meet along a sealing band to retain lubricant within the sealed region. In common practice, the angle between the shaft being sealed and the oil side surface is a steeper angle or of higher numerical degree than is the angle between the air side lip and the shaft being sealed. This arrangement has customarily provided satisfactory sealing in a number of applications, including a certain inherent amount of seal xe2x80x9cpumpingxe2x80x9d effect.
A xe2x80x9cpumpingxe2x80x9d seal is one wherein rotation of the sealed part relative to the seal creates a hydrodynamic action in the sealed fluid at the interface between the seal and the relatively rotatable sealed part. The purpose of this action is primarily to ensure against dynamic leakage and further, to ensure that whatever small amount of fluid that may escape the sealed region is pumped back by this hydrodynamic action into the sealed area.
The primary lips of xe2x80x9cpumpingxe2x80x9d seals are generally formed of solid elastomeric materials such as polyacrylate, fluorocarbon, silicone, nitrile, hydrogenated nitrile, ethylene-acrylate and other similar materials. The seal employs a garter spring to secure a tight fit over the shaft. The garter spring assures an interference of the inner diameter of the primary lip with the shaft wear surface on its outer diameter so that the seal will closely surround the shaft for an extended period of time. The primary lip needs to be stretched to fit onto the shaft in order to ensure effective sealing. Sometimes this can present problems during the installation and wear-in procedure. Additionally, the primary lip seal is difficult to make for bidirectional applications and is not adjustable to varying application conditions.
Thus, there is a need for a primary lip seal with low friction that is flexible, is able to follow the eccentricities in the shaft, has a pumping feature which is able to accommodate pumping action in both directions of shaft rotation, and has the ability to adjust tension in the shaft surface so that the seal can perform properly and yet meet varying application conditions.
The present invention is directed to a rotary shaft seal including a membrane attached to a pair of support rings around a shaft. One of the support rings is adjacent to the other of the support rings. The membrane has a surface in sealing contact with the shaft. A plurality of waves are formed in the surface in response to movement of one of the pair of support rings relative to the other of the pair of support rings to form a pumping spiral whereby any fluid migrating along the shaft is pumped back to the oil side of the seal.
It is an object of the present invention to provide a shaft seal with a membrane which is attached to a pair of spaced apart rings which can be twisted relative to each other so as to form inclined waves on the surface of the membrane in sealing contact with the shaft.
It is another object of the present invention to form inclined waves on the surface of a membrane shaft seal by shear action to form a pumping spiral so that any fluid migrating along the shaft is pumped back to the oil side of the seal.
It is still another object of the present invention to twist a pair of spaced apart support members so that relative movement of one to the other of the pair of support members is induced by friction between the shaft and the sealing surface.
It is another object of the present invention to twist a pair of spaced apart support rings so that relative movement of one to the other of the pair of support members is implemented by an external signal so as to form inclined waves on the surface of the membrane.
It is still another object of the present invention to change the direction of the inclined waves of the surface of the membrane in response to shaft rotation.
It is still a further object of the present invention to provide a low friction shaft seal that permits the use of a wide variety of materials to form the membrane and yet retains the required flexibility to sealingly contact the shaft.
These and other objects and features of the invention will become apparent from the description and especially taken in conjunction with the accompanying drawings illustrating the invention and a preferred embodiment.